Method of producing cyanogen from cuprous cyanide



NIETHOD OF PRODUCING CYANOGEN FROM 'CUPROUS CYANIDE Frank J. Vancheri and Johnstone S. Mackay, Pittsburgh,

Pa., assignors to Pittsburgh Coke & Chemical Company, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Oct. 29, 1958, Ser. No. 770,312

5 Claims. (Cl. 23-151) The present invention relates to the preparation of cyanogen.

It has previously been proposed to prepare cyanogen at relatively low temperatures by the reduction of cupric cyanide to cuprous cyanide and cyanogen. It has also been proposed to heat cupric compounds in the presence of the cyanide ion in aqueous solutions to yield cyanogen. Unfortunately, at the temperatures required for such re actions, the cyanogen:paracyanogen equilibrium favors the polymer. Furthermore, water and acidic gases catalyze the decomposition of cyanogen to paracyanogen.

It is an object of the present invention to prepare cyanogen in increased yields.

Another object is to reduce the formation of paracyanogen in preparing cyanogen.

A further object is to prepare cyanogen from cuprous cyanide.

Yet another object is to avoid the formation of hydrolysis products in the preparation of cyanogen.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

It has now been found that these objects can be attained by heating cuprous cyanide in an inert atmosphere, preferably at atmospheric pressure at a temperature of at least 500 C. and preferably 800-850 C. Higher temperatures can be employed, e.g., as high as 1050 C. At temperatures above 860 C. no paracyanogen can form.

While nitrogen gas is the preferred inert atmosphere, there can also be employed other inert gases such as helium, argon and neon. Yields of cyanogen of 95 to 100% of theoretical are obtained. The inert gas should be dry since water vapor partially hydrolyzes cuprous cyanide to CuOH and HCN.

Unless otherwise stated, all parts and percentages are by weight.

In the following examples 2.5 to 3.0 g. samples were placed in a porcelain combustion boat which was then placed in the center of a one inch diameter Vycor combustion tube, and the tube placed in an electrical combustion furnace. A plug of glass wool was placed at the exit of the tube. The tube and contents were weighed on a trip scale. At the entrance of the tube was a rubber stopper with a glass tube exit which was connected with rubber tubing to a gas scrubber containing 200 ml. of 1% sodium hydroxide solution.

-A slow stream of nitrogen, 70-100 cc./ntin., was passed through the tube and the bed was gradually heated to the desired temperature, e.g., 820 C., using a 45 to 60 minute heat-up time. The temperature was recorded with a thermocouple and a potentiometer. 'Ihe cuprous 2,957,751 Patented a. 25, 1950 a cyanide was held on temperature for 0.5 to 3.0 hours. To prevent air from getting into the tube and oxidizing the copper residue, thenitrogen stream was left on during cooling.

5 The tube was weighed and the weight loss recorded. The residue in the boat was metallic copper. The caustic solution was diluted to 250 ml. and a 50 ml. aliquot was titrated for cyanide with 0.1 N silver nitrate. Cyanogen, based on the hydrolysis reaction:

( CN) +H O- HCN-l-HCNO was calculated and the molar yield reported. Also, CuCN was decomposed and the gases were condensed in a Dry Ice-acetone trap. The M.P. of the condensed liquid was 26 to -34 C. The reported M.P. of cyanogen is -34.4 C.

EXAMPLE 1 Into the porcelain combustion boat was weighed 2.7987 grams of cuprous cyanide. The boat was placed in the center of the combustion tube which in turn was heated by the furnace. A slow stream of dry nitrogen was passed through the tube and the bed gradually heated to 820 C. The reaction was held at this temperature for 3 hours and the gases swept out of the tube and collected in the gas scrubber containing 200 ml. of 1% sodium hydroxide as previously indicated. Cyanogen was obtained in an amount of 0.797 g. which was 98.8% of theory. 2.0 g. of metallic copper was recovered from the combustion boat.

The effect of temperature on the yields can be seen from the following table in which the reaction conditions were identical with those of Example 1 except for the indicated changes.

Table 1 Temper- CuCN (ON 3 Yield Example ature (g.) (g.) 11%]??? .0

1 A trace of Water in the nitrogen gas in this run resulted in a slightly higher than theoretical reported yield.

From this table, it can be seen that using a reaction time of 3 hours at 820 0., there was obtained a yield of over 98% cyanogen, while as the temperature was lowered the yield was reduced.

The effect of time of reaction is shown in Table 2 where all reactions were carried out at 820 C.

Table 2 Time CuCN (ON), Yield Example (hr.) (g.) (g.) Percent What is claimed is: l. A process of preparing cyanogen comprising heat- 7 ing cuprous cyanide in an inert atmosphere at a temperature of at least 500 C.

2. A process of preparing cyanogen comprising heating cuprous cyanide in an inert atmosphere at a temperature of at least 800 C.

3. A process according to claim 2 wherein the inert atmosphere is nitrogen gas.

4. A process according to claim 2 wherein the tem- 5 perature is 800 to 850 C.

5. A process according to claim 4 wherein the inert atmosphere is nitrogen gas and the reaction is carried out at atmospheric pressure.

References Cited in the file of this patent Williams: The Chemistry of Cyanogen Compounds and Their Manufacture and Estimation, publ. by J. and A. Churchill, London, 1915, page 3. 

1. A PROCESS OF PREPARING CYANOGEN COMPRISING HEATING CUPROUD CYANIDE IN AN INERT ATMOSPHERE AT A TEMPERATURE OF AT LEAST 500*C. 